1. Field of the Invention
The present invention relates to a component built-in circuit substrate formed by laminating plural wiring layers, where electronic components are mounted on the core layer (i.e. an inner layer out of the wiring layers), and to a method of producing the component built-in circuit substrate.
2. Background Art
With higher functionality and downsizing of electronic devices in recent years, higher packaging density tends to be demanded in a substrate with electronic components mounted thereon. Accordingly, as a printed circuit substrate used for mounting electronic components, what is called a component built-in circuit substrate is used, where electronic components are mounted on an inner layer (core layer) out of plural laminated wiring layers (refer to patent literature 1 for example). Patent literature 1 shows an example where a chip component (electronic component with a pair of terminals) such as a chip capacitor is mounted on an inner layer out of plurally provided wiring layers in a printed circuit substrate. Here, the terminal of a chip component is soldered to a mounting land with a solder resist formed therearound in the inner layer, and a solder resist unformed part is provided between adjacent mounting lands.
In patent literature 1, however, the following disadvantages occur caused by a solder resist being formed in an exposed state and by a range in which the solder resist is formed. Specifically, in producing a component built-in circuit substrate with plural wiring layers laminated thereon, an inner layer after components are mounted thereon needs to undergo roughening process to improve adhesion between an interlayer insulating layer and the inner layer. The roughening process is performed with a chemical solution such as strong acid and strong alkali, which inevitably damages a solder resist in its exposed state. In laminating and heating process for forming an interlayer insulating layer, imperfect filling is likely to occur in which resin does not completely enter a solder resist unformed part between mounting lands. If reheating is executed to mount an electronic component onto an outer layer with the imperfect filling remaining, a defect such as a bridge (solder for joining terminals together is remelted to short-circuit between the terminals). In this way, a conventional component built-in circuit substrate with a chip component contained causes various kinds of defects resulting from a shape in which a solder resist is formed.
[Prior Art Document]
[Patent Literature]
    [Patent literature 1] Japanese Patent Unexamined Publication No. 2007-214230